This invention relates generally to a gas circuit breaker, and, more particularly, to a puffer-type gas circuit breaker having a puffer chamber and a thermal puffer chamber.
There has been proposed a puffer-type gas circuit breaker which includes a puffer chamber for compressing an arc extinguishing gas for blow-out in connection with the interrupting operation, and a thermal puffer chamber for increasing the pressure of the arc extinguishing gas for blow-out by the energy of an arc produced when contacts are apart from each other. Such a puffer-type gas circuit breaker is disclosed, for example, in Japanese Patent Unexamined Publication No. 2-12982, and this circuit breaker is shown in FIG. 14.
The puffer-type gas circuit breaker of FIG. 14 comprises a fixed contact 1, a movable contact 2 disposed in an opposed relationship with respect to fixed contact 1 so as to come into contact therewith, a drive shaft 11 for driving the movable contact 2 toward and away from the fixed contact 1, a fixed piston 12, a puffer cylinder 13, slidably fitted on the fixed piston 12, and first and second insulating nozzles 5 and 6 connected to the puffer cylinder 13 and surrounding the movable contact 2. The fixed piston 12, the drive shaft 11 and the puffer cylinder 13 cooperate with one another to define a puffer chamber 7 within the puffer cylinder 13. A second gas flow passage 18b is formed between the first and second insulating nozzles 5 and 6, and is in communication with a thermal puffer chamber 8. The thermal puffer chamber 8 is separated from the puffer chamber 7 by a partition member 25 provided inside the puffer cylinder 13 A first gas flow passage 18a is formed between the movable contact 2 and the first insulating nozzle 5 and also between the movable contact 2 and the partition member 25. The first gas flow passage 18a is in communication with the puffer chamber 7.
When the drive shaft 11 is driven to the right in FIG. 14, the movable contact 2 is brought out of contact with the fixed contact 1, so that an arc 16 is produced between these two contacts In connection with this rightward movement of the drive shaft 11, the arc extinguishing gas within the puffer chamber 7 is compressed into a high pressure. Also, the arc extinguishing gas within the thermal puffer chamber 8 is heated by the thermal energy of the arc 16, and therefore is brought to a high pressure.
Then, the highly-pressurized arc extinguishing through the first gas flow passage 18a, and also the highly-pressurized arc extinguishing gas within the thermal puffer chamber 8 is blown onto the arc 16 through the second gas flow passage 18b, thereby effecting the arc extinguishing operation.
If the above puffer-type gas circuit breaker is so designed that a medium and a small electric current can be mainly interrupted by the blowing of the arc extinguishing gas from the puffer chamber 7 and that large electric current can be mainly interrupted by the blowing of the arc extinguishing gas from the thermal puffer chamber 8, the circuit breaker can be of a compact construction.
However, if the volume of the thermal puffer chamber 8 is increased in order to enhance the interrupting performance and particularly the large current-interrupting performance, the space of the puffer chamber 7 that can be utilized for the compression is naturally reduced as is clear from FIG. 14, and this lowers the pressure rising characteristics of the puffer chamber 7. The pressure rising characteristics can be maintained by increasing the volume of the puffer chamber 7. Namely, this can be achieved by increasing the diameter of the puffer cylinder 13. With such a construction, however, the pressure receiving area of the puffer cylinder 13 increases, which results in a drawback that the operating force for driving the drive shaft 11 is increased.